A router is a network component that directs messages received on one of its ports to one or more of the other router ports according to the destination information contained in the message. Routers typically segment a network into subnets whereas a switch provides connectivity within a subnet. A router represents a shared communication path in the network. Routers resolve this resource contention by queuing messages until the shared resource or the receiving subnet is free.
A router potentially introduces multi-millisecond fluctuations in the latency between the 1588 master clock and a 1588 slave clock. Uncorrected these fluctuations will cause synchronization errors. The magnitude of these fluctuations do not permit the straightforward application of IEEE 1588 to achieve the highest synchronization accuracy. To achieve the highest accuracy IEEE 1588 specifies that the subnets defined by a router be spanned by an IEEE 1588 Boundary Clock. The example shown on the home web page illustrates a boundary clock spanning a router that defines two subnets. Experiments with prototype implementations of IEEE 1588 Boundary Clocks indicate that these boundary clocks enable cross subnet synchronization accuracies equivalent to those obtainable within a subnet.